Where should normals be facing
It's important to have the normal pointing outward of your model, otherwise back face might be visible at render time and give bad visual effect.

The reason blender still allow normal to be calculated inside is for specific use case like rendering a room from the inside.

However, when there is something wrong with a model, blender might have a bad time computing the normal and you might have to flip them manually if some if them are wrong.

I can help you more if you post screenshots or share your blend file.

Update new that I have seen the blend file :

You faces were indeed inward, you can see that by going in edit mode and activating the face orientation visualization tool ( red is the back of the face, blue is the front, so red should never be in render sight ) :



The reason Blender is having trouble computing the orientation is because your model is "open" at the hands, neck and bottom, that kind of hole should not appear in your final model. If you don't want to add more geometry I would suggest using the solidify modifier, it will simply add some thickness to the planes and red faces won't appear anymore.



Or if you want simply want to have the faces in the correct orientation as a quick fix just select every faces and perform a flip normals operation.